Schallert starred in an innovative 1964 TV pilot for ABCPhilbert, which combined live action camera work and animation. Created by Friz Freleng and directed by Richard Donner, ABC backed out of the series shortly before full production was to begin, though the completed pilot was released in theaters as a short subject.

In addition to his onscreen performances, Schallert has done voiceover work for numerous television and radio commercials over the years. Among these were a recurring role as "Milton the Toaster" in animated commercials for Kellogg's Pop-Tarts.

Schallert was president of the Screen Actors Guild from 1979 to 1981 (his former co-star and television daughter, Patty Duke, would follow him from 1985 to 1988).